1. Field of the Invention
The present invention relates to a light emitting diode (LED) and more particularly to a method for fabricating the LED and the structure thereof.
2. Description of the Prior Art
LED is a solid-state semiconductor device, which makes use of the recombination of two charged carriers by electrical current flowing through a diode, to release energy in the form of light, featuring advantages of compact in size, fast response, and high efficiency. Therefore LED has versatile applications to a variety of industries.
Due to its compact size, LED can be used for various applications. For example, the LED has gained great popularity for lighting application. Moreover, the demand for white LED has been substantially boosted. White light is produced by blending multiple colors in the visual spectrum. The white light visible to the human eyes is formed by mixing at least two colors of different wavelengths in appropriate intensities, for instance: tri-wavelength white light blended by red, green and blue colors, or bi-wavelength white light blended by blue and yellow colors.
There are two most common techniques in obtaining white LED by mixing blue and yellow lights. The first method is to place a blue LED die and a yellow LED die together to mix uniform white light by proper control of electrical current through each LED die. Even though the technique has good luminescent efficiency, the difference in current control and variations in decay rate of dies surely deteriorate the luminescent efficiency of the LED. The other art is based on the emission of blue light which excites the yellow phosphor to emit yellow light, resulting apparent white light via mixing blue and yellow light. Due to ease in production and low cost, a majority of white LED manufacturers adopt this approach. Conventional method of generating white light from the blue light to excite yellow phosphor incorporates the phosphor with a packaging substrate in the package of LED die. The above mention method is strictly depended on high specific weight of phosphor, the uniformity of phosphor will affect the efficiency of excited the phosphor. An extra diffusion layer can be coated outside the package substrate, therefore, the refraction of micro transparent particles or bubbles spreading in the diffusion layer can uniform the blended light. However, materials of the micro transparent particles or bubbles and distribution densities of the particles should be carefully matched. Therefore, there are unexpected factors embedded in the foregoing art, and great difficulties are surely found once in carrying out the manufacturing.